Skip the Electrek summary and scroll down to the memo itself. It’s a cogent and fascinating read:

Most of the design tolerances of the Model 3 are already better
than any other car in the world. Soon, they will all be better.
This is not enough. We will keep going until the Model 3 build
precision is a factor of ten better than any other car in the
world. I am not kidding.

Our car needs to be designed and built with such accuracy and
precision that, if an owner measures dimensions, panel gaps and
flushness, and their measurements don’t match the Model 3 specs,
it just means that their measuring tape is wrong.

Some parts suppliers will be unwilling or unable to achieve this
level of precision. I understand that this will be considered an
unreasonable request by some. That’s ok, there are lots of other
car companies with much lower standards. They just can’t work
with Tesla.